The invention relates to a device for measuring a fill level in a container with an ultrasound sensor, wherein the ultrasound sensor has allocated to it a damping beaker with at least one antechamber, and the antechamber has an inlet opening to the container and an outlet opening to the damping beaker.
Predominantly ultrasound sensors are used to determine the oil level in engines. These emit sound waves, which are reflected at the interface between two media, e.g., gas and oil, wherein fluids other than oil can also be measured, and again received by the ultrasound sensor. The fill level in the container having the device can then be derived from the determined runtime of the sound waves. However, the fill level is difficult if not impossible to determine when an engine is operational, in particular one in a motor vehicle, since the oil is highly foamed, and the sound waves are reflected by the gas bubbles in the oil. As a result, there is a very wide scattering of detected values.
However, a distinct interface must be present between the gas and oil media for evaluable measurements. In order to counter the problem of widely scattering values, damping devices, e.g., so-called damping beakers, are allocated to the ultrasound sensors. These damping beakers envelop the measuring section of the ultrasound sensor, and the fluid to be measured therein is calm, and only a small opening in the damping beaker to the container connects it with the latter. Fewer gas bubbles get into the damping beaker through the small opening in the damping beaker to the container. The fill level in the damping beaker here reflects the liquid level outside of the damping beaker.
Publications DE 10 2008 027 969 A1 and WO 2008/009277 A1 show further developments of such a damping beaker. A pre-volume allocated to the damping beaker in both publications. These pre-volumes are used to degas the fluid to be measured, e.g., foamed oil, so that a fluid relatively free of bubbles flows into the measuring section of the damping beaker. The pre-volumes are here designed in such a way as to guide the fluid in a plane through the structures arranged in the chambers to the inlet opening of the damping beaker.
However, tests revealed that the foamed oil in an engine streams through the known pre-volumes and chambers very rapidly given sudden jumps in speed, e.g., from 3000 to 4000 or 5000 RPM, without it being possible to degas the foamed oil in the pre-volumes. Therefore, gas bubbles are introduced into the measuring section of the damping beaker, impeding the correct display of the fill level. Since these gas bubbles can only slowly escape the measuring section of the damping beaker, the known sensors do not detect the actual fill level in the container even long after the jumps in speed, even though a measurable fill level is present outside the damping beaker.
The time for which the fill level is not correctly determined is called the dead time, and potentially leads to an error message indicating too low a fill level in the container. This problem is encountered in particular given a dynamic driving style over a longer period, since the long dead times in which the actual fill level is not determined eliminates the ability to calculate an average value, as a consequence of which “wrong actions” stemming from the untrue error message can result in major damages.